The proliferation of DC powered and charged mobile/portable products has resulted in connecting these products to a vehicle""s electrical system during all states of vehicle operation. Prior to the miniaturization of these products, the electrical power for operating or charging was from AC sources. AC power, although highly controlled, still produces significant fluctuations, transients and electrical noise. AC power conditioning is most often provided through a separate power conditioning device, commonly referred to as a surge and spike protector. AC power conditioning devices protect sensitive circuits from voltage spikes caused by lightning, electrostatic discharge and power surges caused by power grid interruptions and other potentially dangerous live transients.
12-volt direct current(DC) is potentially a more variable and complex electrical environment than traditional AC sources. The Society of Automotive Engineers(SAE) has defined the electrical environment in SAE specification SAE 1113/11, Section 8, Test Pulses and Appendix B, Test Severity Levels. Some examples from Section 8 and comments follow.
Although a normally operating vehicle will maintain a supply voltage of 11-16 VDC, many conditions occur which cause much larger voltage variations, ranging as low as 4.5 VDC to transients as high as 286 VDC with spikes varying from xe2x88x92150V to xe2x88x92600V. The vehicle circuits for some DC power outlets and cigarette lighter sockets are partially protected from adverse power conditions through a switch that disconnects the outlets from the line during engine starting. However, potentially damaging electrical transients, surges, spikes, and noise continue to exist within the vehicle power system.
Other surges and spikes occur because not all DC power outlets are disconnected from the battery during starting. Under very cold discharged battery conditions, the very large voltage swings, from 4.5 to 16 VDC, cause surges and large transients as vehicle systems are energized. Failure of the DC supply, through alternator control loss, and the switching of heavy vehicle loads, such as lights and air conditioning, are also primary sources of transients, over-voltage and induced spikes.
In SAE J1211, Table 3, SAE has summarized the four principle types of transients found in automotive wire harnesses. The transients and the possible effects on electronic devices is noted as follows:
Unattended attachments of portable devices to a vehicle electrical system create another unusual condition for vehicle operation. Whereas the AC power sources are considered inexhaustible and continued attachment of portable products has no negative effects on the source; quite the opposite exists regarding vehicle power where the battery must retain sufficient energy to start the vehicle.
The automotive electrical environment can be electrically hazardous to connected equipment, such as cellular telephones, video equipment and computers, whose batteries are charged from the cigarette lighter through an adapter or powered directly from the vehicle DC power. The SAE, in paragraph 1.1 of SAE J1113/11 states as follows: xe2x80x9cInstalled electrical equipment is powered from sources which contain, in addition to the desired electrical voltage, transients with peak values many times this value, caused by the release of stored energy during the operation of a relay and/or other loads connected to the source while starting and/or turning off the vehicle.xe2x80x9d
SAE Standard J1113/11 defines tests which are to be conducted to replicate the potential conducted transients developed in 12 volt DC powered passenger cars, light trucks and heavy duty trucks. The need and value of the Power Supply is evident by the recommended test voltages contained in J1113/11, Table 3. Test pulse parameters require test pulses from xe2x88x9225 to xe2x88x92100V for passenger cars and light duty trucks; xe2x88x9211 to xe2x88x92600V for 12 volt system heavy duty trucks. Other specified test pulse conditions are equally or more severe.
Many adapters or connected input circuits cannot tolerate the large voltage spikes that can occur when a vehicle is jump started, or when its battery is disconnected while the car is running. Even window, heater, and starter motors can generate spikes well beyond the normal range of battery voltage.
It is a primary object of the present invention to provide a portable DC Power Supply for portable electronic components on board a vehicle that protects both the portable components as well as the vehicle""s electrical system.
In accordance with the present invention, a DC Power Supply is provided for portable electronic components on board a vehicle that protects both the portable components as well as the vehicle""s electrical system including circuitry to sense and suppress voltage spikes or current surges and to disconnect the female cigarette lighter receptacles when the vehicle power outlet voltage drops below a preset threshold.
The power supply has sensing, switching and optimal control circuits that sense voltage spikes, current surges and other abnormalities in the vehicle""s electrical systems and rapidly directs excess voltages, suppresses current surges and responds to other electrical abnormalities before they can reach the power input connector of the connected devices. When optional features such as low voltage protection are added to the circuits, the power supply disconnects the power to connected devices when the vehicle""s voltage to the power supply falls below preset thresholds. Short circuit and overload protection is provided through foldback circuitry or fusings.
Toward these ends the present power supply includes a DC surge and spike and an optional low voltage protector for attachment to vehicular electrical systems for powering electrical devices such as computers, audio and video products, PDA""s, wireless phones, and other electronic devices, including in one embodiment, a housing having a plug connector insertable into an on-board outlet, a plug receiving type outlet in the housing, and a circuit in the housing having a main FET switch that redirects excess voltage when it senses rapidly rising voltage at the input, and also disconnects the input from the output when input voltage falls below a threshold value.
The circuit operates by redirecting excess voltage from the vehicle""s electrical system at the first sign of a voltage spike. A programmable shunt regulator is used to sense the rapidly rising voltage as well as steady-state voltage above a setpoint. After a time delay, the main switch begins to turn on again and if the input voltage is still high, the circuit acts as a series regulator, allowing the load to see only a set point voltage.
The circuit also protects the vehicle""s battery by turning the main switch off when battery voltage falls below safe levels. However, the load should not be disconnected prematurely by a transient voltage drop that occurs in some vehicles at start-up. A second programmable shunt regulator responds to low input voltage by drawing less current, which shunts gate drive away from the main switch FET.
Other objects and advantages will appear more clearly from the following detailed description.